Application of Finite Element Analysis in Multiscale Metal Forming Process

The application of finite element analysis has been presented in multiscale metal forming process. A 3D finite element method (FEM) has first been proposed to analyze the deformation mechanism of thin strip cold rolling with the consideration of friction variation in deformation zone. The crystal plasticity finite element method (CPFEM) is applied on the simulation of surface asperity flattening in the uniaxial planar compressing process. 3D Voronoi tessellation and frictional modeling have been applied in microforming processes. All simulation results from the proposed modeling have been validated by the related experimental results

Analysis of thin strip profile during asymmetrical cold rolling with roll crossing and shifting mill

Strip profile control during rolling is required to assure the dimensional quality of rolled thin strip is acceptable for customers. Throughout rolling, the strip profile is controlled by using the advanced shape control rolling mill, such as the combination of work roll crossing and shifting during asymmetrical rolling, the one of the valuable methods to control the strip profile quality in rolling process. In this paper, the influences of cold rolling parameters such as the crossing angle and axial shifting value of work rolls on the strip profile are analysed. The strip shape control is discussed under both symmetrical and asymmetrical rolling conditions. The obtained results are appropriate to control the rolled thin strip profile in practice. (2014) Trans Tech Publications, Switzerland

Effect of mesh on springback in 3D finite element analysis of flexible microrolling

In flexible microrolling, springback in thickness direction is a critical indicator to determine the forming quality. Accurate prediction of springback is one of the significant aspects in the finite element analysis of flexible microrolling. Meshing is a step of great importance in finite element analysis of manufacturing process as it directly determines the accuracy of the FEA results as well as the requested computational time. This paper presents a numerical study on revealing the mesh effects on the accuracy of springback estimation utilising ABAQUS/Standard for modelling and analyses. Two types of meshes with six mesh sizes for each mesh type are considered in this study and the optimal mesh type and mesh size have been found to obtain accurate value of springback while saving as much computational time as possible

Al-Cu Composite’s Springback in Micro Deep Drawing

With the recent technological trend of miniaturization in manufacturing industries, the rise of micro forming operations such as micro deep drawing (MDD) is inevitable. On the other hand, the need of more advanced materials is essential to accommodate various applications. However, a major problem are size effects that make micro scale operations challenging. One of the most important behaviors affected by size effects is the springback phenomenon, which is the tendency of a deformed material to go back to its original shape. Springback can affect dimensional accuracy, which is very important in micro products. Thus, this paper investigated the springback behavior of Al-Cu composite in MDD operations. Micro cups were fabricated from blank sheet specimens using an MDD apparatus with variation of annealing holding time. The springback values were measured and compared to each other. The results showed that different grain sizes lead to variation in the amount of springback. However, unlike in single-element materials, the amount of springback in Al-Cu composite is not only related to the thickness to grain size (t/d) ratio. Another factor, i.e., the existence of an interfacial region between layers, alters the mechanical behavior of the composite

Analysis of contact mechanics in micro flexible rolling

Micro flexible rolling is a new microforming method by online controlling and adjusting the roll gap to make various strip thickness in the submillimeter range. The micro flexibly rolled strips can be divided into three zones of the thicker zone, the thinner zone and the transition zone after experiencing the upward and downward rolling processes. However, it is tough to achieve the final target thickness especially in the transition zone due to a number of issues relating to the contact mechanics such as the change in the central neutral point/zone, the touch at the edges of the work rolls, the elastic deformation of the work rolls, the roll bite arc modifications in real time and the tribological conditions. All of these factors have significant influences on flatness, profile and surface finish of the rolled products, as well as the rolling forces. In the current work, a new model has been developed in order to clarify the micro flexible rolling process. This model considers a non-circular contact arc which includes an elastic loading region at the start of the roll gap, a plastic reduction region with backward slip, a central flattened region without slip, the plastic reduction region with forward slip, and an elastic unloading region at the end of the roll gap. In this study, the effect of speed ratio (the ratio of the lifting speed and the rolling speed) on the dimensions and the rolling forces along the transition zones is investigated. The contact mechanics in the micro flexible rolling are systematically analysed. The simulation results are found to be in line with the experimental ones, which means that the developed model with high precision is suitable for the analysis of the micro flexible rolling process

Experimental study on adhesion of oxide scale on hot-rolled steel strip

An experimental method was developed to study the adherence properties of the oxide scale formed on microalloyed low carbon steel after hot strip rolling. The evolution of the oxide scale during laminar cooling was investigated using Gleeble 3500 Thermal-Mechanical Simulator connected with a humid air generator. After the sample cooled down to ambient temperature, the oxide scale was protected by lacquer to prevent the scale from losing. Physicochemical characteristics of the oxide scale were examined and the adherence mechanism was discussed. Decomposed wustite a mixture of α-iron and magnetite (Fe3O4), can substantially improve the integrity of oxide scale. However, large quantities of hematite (Fe2O3) or retained wustite (FeO) were found detrimental to the adhesion of the oxide scale. It is found that the adherence of oxide scales significantly depends on the phase composition of oxide scales with different thickness

Analysis of axisymmetric cup forming of metal foil and micro hydroforming process

A novel forming method micro hydromechanical deep drawing (MHDD) is focused to improve the tribological property and forming limit. In this study, a theoretical model for MHDD is developed to investigate the size effect on deformation behavior in micro hydromechanical deep drawing. The effects of fluid pressure, the difference of friction coefficients at inner pockets and outer pockets are considered in the investigation on the size effect of tribological property. The friction force decreases as the scale factor decreases in MHDD process. It is also found that the tribological property in micro scale can be improved by applying the fluid pressure. The forming limit decreases as the relative punch diameter increases. However, it is clarified that the forming limit can be improved by decreasing the friction force in MHDD

Study on micro hydro-mechanical deep drawing using finite element method

A numerical model was established to investigate the micro hydro-mechanical deep drawing process of austenitic stainless steel 304 foil (0.05 mm thickness). Due to the miniaturisation of the specimen size, the effect of grain size, gap distance and radial pressure during drawing process could be prominent. The results indicate that the appropriate radial pressure and gap distance could improve the limit drawing ratio (LDR) of manufactured cylindrical cups by reducing the friction resistance. The maximum LDR obtained in the present work reaches 3.2, which is much higher than that obtained by conventional deep drawing process

Two Piggybacking Codes with Flexible Sub-Packetization to Achieve Lower Repair Bandwidth

As a special class of array codes, $(n,k,m)$ piggybacking codes are MDS codes (i.e., any $k$ out of $n$ nodes can retrieve all data symbols) that can achieve low repair bandwidth for single-node failure with low sub-packetization $m$. In this paper, we propose two new piggybacking codes that have lower repair bandwidth than the existing piggybacking codes given the same parameters. Our first piggybacking codes can support flexible sub-packetization $m$ with $2\leq m\leq n-k$, where $n - k > 3$. We show that our first piggybacking codes have lower repair bandwidth for any single-node failure than the existing piggybacking codes when $n - k = 8,9$, $m = 6$ and $30\leq k \leq 100$. Moreover, we propose second piggybacking codes such that the sub-packetization is a multiple of the number of parity nodes (i.e., $(n-k)|m$), by jointly designing the piggyback function for data node repair and transformation function for parity node repair. We show that the proposed second piggybacking codes have lowest repair bandwidth for any single-node failure among all the existing piggybacking codes for the evaluated parameters $k/n = 0.75, 0.8, 0.9$ and $n-k\geq 4$

Friction and asperity contact in strip rolling

This paper reviews different aspects of friction and asperity contacts in strip rolling. The mixed film lubrication model considers the effect of asperity flattening and the lubrication within the working zone. The oil concentration of the emulsion at entry and throughout the roll bite is considered together with the thermal effects of the contacts. The actual area of contact due to asperity deformation can be determined from a 3-wavelength FEM model. The deformation of a randomly generated surface of the hot strip with oxide scale can also be modeled by an FEM method. The friction variation in the roll bite can be determined by a sensor roll, and the average friction determined from the forward slip by the marking method or laser Doppler method. The friction models in FEM modeling are also discussed